The present invention relates to a method for reducing the viscosity of crude oils and crude oil residuum by mineral acid enhanced thermal treatment of crude oil or crude oil residuum. The product from the combination of acid and thermal treatment process affords oil with a substantially lower viscosity than the starting oil or product oil derived from thermal treatment without acid addition.
Thus, the instant process provides an improved visbreaking method and can be utilized as an upgrading process in pipeline transportation, or to reduce the viscosity of a water-in-oil emulsion used in enhanced oil recovery (EOR) operations.
Technologies for viscosity reduction of heavy crude oils and resids are of importance to the upstream and downstream petroleum businesses respectively. In downstream refining operations, visbreaking and hydro-visbreaking (visbreaking with hydrogen addition) of resids are known in the art and practiced commercially. In the upstream production operations, crude oil dilution with gas condensate and emulsification technologies using caustic and water are some of the commonly practiced art in pipeline transportation of heavy oils e.g., bitumen. Moreover, viscosity reduction of heavy crude oils can play a role in new upstream technology related to recovering hydrocarbons from subterranean formations using enhanced oil recovery methods. There is a continuing need in the oil industry for technologies and technology improvements relating to viscosity reduction of crude oils and resids.
The depletion of reserves containing high quality crude oil, and the accompanying rise in costs of high quality crude oil has producers and refiners of petroleum looking to heavy crude oil reserves as a source for petroleum. There are many untapped heavy crude oil reserves in a number of countries including Venezuela, Chad, Russia, the United States and elsewhere. However, these heavy crude oils, because of their high viscosity and poor flow properties, pose significant challenges to producers, transporters and refiners of oil. Heavy crude oils are often difficult if not impossible to extract from subterranean formations in an efficient and cost-effective manner. Further, even when the heavy crude is extracted, the poor flow characteristics of the crude oil present additional complications in pumping, transporting and refining the crude oil.
Processes have been developed to aid in extracting the heavy crude from underground reservoirs. For instance, a new process has recently been developed which aids in extracting heavy crude oil from a subterranean formation, which uses solids-stabilized emulsions as a driver fluid or as a barrier fluid to help recover hydrocarbons from the subterranean formation. These methods are generally discussed in U.S. Pat. Nos. 5,927,404, 5,910,467, 5,855,243, and 6,068,054. U.S. Pat. No. 5,927,404 describes a method for using the novel solids-stabilized emulsion as a drive fluid to displace hydrocarbons for enhanced oil recovery. U.S. Pat. No. 5,855,243 claims a similar method for using a solids-stabilized emulsion, whose viscosity is reduced by the addition of a gas, as a drive fluid. U.S. Pat. No. 5,910,467 claims the novel solids-stabilized emulsion described in U.S. Pat. No. 5,855,243. U.S. Pat. No. 6,068,054 describes a method for using the novel solids-stabilized emulsion as a barrier for diverting the flow of fluids in the formation. In a solids-stabilized emulsion, the solid particles interact with the surface-active components in the water and crude oil to enhance the stability of the emulsion. The process is simple in that the emulsion is made by simply mixing oil, typically crude oil from the reservoir itself, with micron or sub-micron sized solid particles and mixing with water or brine until the emulsion is formed. The process is also cheap in that all of these materials should be readily available at the reservoir site.
Solids-stabilized water-in-oil emulsions have a viscosity that is greater than that of the crude oil to be recovered, and as such, can serve as an effective drive fluid to displace the crude oil to be recovered, such as described in U.S. Pat. Nos. 5,927,404, and 5,855,243.
The solids-stabilized water-in-oil emulsions can also be used as a barrier fluid, to fill in subterranean zones of high rock permeability, or xe2x80x9cthief zones.xe2x80x9d When drive fluid is injected into a reservoir, the injected drive fluid may channel through these zones to producing wells, leaving oil in other zones relatively unrecovered. A high viscosity barrier fluid, such as the solids-stabilized water-in-oil emulsion, can be used to fill these xe2x80x9cthief zonesxe2x80x9d to divert pressure energy into displacing oil from adjacent lower-permeability zones.
However, sometimes the solids-stabilized water-in-oil emulsion is too viscous to be injected or is too viscous to otherwise be efficiently used as a drive or barrier fluid. Therefore, there is a need to be able to reduce the viscosity of the emulsion to obtain the optimum rheological properties for the type of enhanced oil recovery method used and for the particular type and viscosity of crude oil to be recovered.
Viscosity reduction of heavy oils is also important for downstream operations. Transporters and refiners of heavy crude oil have developed different techniques to reduce the viscosity of heavy crude oils to improve its pumpability. Commonly practiced methods include diluting the crude oil with gas condensate and emulsification with caustic and water. Thermally treating crude oil to reduce its viscosity is also well known in the art. Thermal techniques for visbreaking and hydro-visbreaking are practiced commercially. The prior art in the area of thermal treatment or additive enhanced visbreaking of hydrocarbons teach methods for improving the quality, or reducing the viscosity, of crude oils, crude oil distillates or residuum by several different methods. For example, several references teach the use of additives such as the use of free radical initiators (U.S. Pat. No. 4,298,455), thiol compounds and aromatic hydrogen donors (EP 175511), free radical acceptors (U.S. Pat. No 3,707,459), and hydrogen donor solvent (U.S. Pat. No 4,592,830). Other art teaches the use of specific catalysts such as low acidity zeolite catalysts (U.S. Pat. No. 4,411,770) and molybdenum catalysts, ammonium sulfide and water (U.S. Pat. No. 4659453). Other references teach upgrading of petroleum resids and heavy oils (Murray R. Gray, Marcel Dekker, 1994, pp.239-243) and thermal decomposition of naphthenic acids (U.S. Pat. No. 5,820,750).
A common thread that knits the various methods previously described is a need to obtain optimum viscosity reduction in oil.
It is this aspect of enhancing viscosity reduction that this invention addresses. Provided is a method of reducing the viscosity of oil or a water-in-oil emulsion by an acid enhanced thermal treatment process. The product from the acid enhanced thermal treatment process has a substantially lower viscosity than the untreated oil or the untreated water-in-oil emulsion, respectively.
An embodiment of the invention is directed to a method for decreasing the viscosity of crude oils and residuum comprising the steps of:
(a) contacting the crude oil or residuum with an effective amount of an acid consisting essentially of acid,
(b) heating said crude oil or crude oil residuum and said acid at a temperature and for a time and at a pressure sufficient to decrease the viscosity of said crude oil or residuum.
As used herein, crude oil residuum is defined as residual crude oil obtained from atmospheric or vacuum distillation.
As used herein, the process comprises, consists and consists essentially of the steps herein described.
Another embodiment of the process is directed to a thermal visbreaking method for reducing the viscosity of crude oils and crude oil residuum by thermally treating the oils and residuum wherein the improvement comprises contacting the crude oil or residuum with an effective amount of an acid consisting essentially of or consisting of acid and heating said crude oil or residuum and said acid at a temperature and for a time and at a pressure sufficient to decrease the viscosity of said crude oil or residuum.
The invention is also directed to a crude oil or crude residuum having decreased viscosity prepared by
(a) contacting the crude oil or residuum with an effective amount of an acid consisting essentially of acid,
(b) heating said crude oil or residuum and said acid at a temperature and for a time and at a pressure sufficient to decrease the viscosity of said crude oil or residuum.
Another embodiment of the invention is directed to a method of preparing a water-in-oil emulsion with a decreased viscosity comprising the steps of:
(a) contacting the oil with acid,
(b) heating said oil and said acid at a temperature and for a time and at a pressure sufficient to decrease the viscosity of said oil, and
(c) adding water and mixing until said water-in-oil emulsion is formed.
A solids-stabilized emulsion having a reduced viscosity may also be made using this method by adding solid particles to the oil after the step of heating the acid treated oil (step b), but before emulsification by adding water and mixing (step c).